Color cathode ray image display system



June 28, 1960 s. ROBERTS 2,943,232

COLOR CATHODE: RAY IMAGE DISPLAY SYSTEM Filed Feb. 16, 1959 3 Sheets-Sheet 1 His Attorney. i

June 28, 1960 s. ROBERTS coLoR cATHoDE RAY IMAGE DISPLAY SYSTEM 3 Sheets-Sheet 2 Filed Feb. 16, 1959 11 1111111 H r v v w/ AAAI Inventor-: Shepard Faber-s,

.by il@ June 28, 1960 s. ROBERTS ooLoR cATHonE: RAY IMAGE DISPLAY .SYSTEM 3 Sheets-Sheet 3 Filed Feb. 16, 1959 fr) Venter: Sh epa r-d Robers a 2,943,232- oLoR cArHoDE RAY IMAGE DISPLAY SYSTEM hepard" Roberts,Scotia, N.Y., assignor to 'General Eleca tric Company, a corporation of New York Filed Feb. 16, 19159, ser. No. 193,578

f 13,claims. (cl. 315-13) invention pertains to a, color cathode ray image display system of the type in whichelectron streams of dieringvelocities impinge upon a viewing screen to excite .dilerent phosphor layers producing light fof dilferent colors, respectively. Cathode ray tubes utilized in such V 'emmaybe denominated as Penetron multilayer type olortubesa y," Y, Y a

In this ,form of color cathode rayrtube', theviewing vsljeenV isrprovidedwith phosphors that are Vselectively excited by `cathode ray orY electron `beams of `dilfering velocities. One phosphor layer, for example, may pro,- duce` blue'light when struck by electrons of a 201cv. electron beam. Anotherqmay produce yellow light when struckj by electronsof a kv. electron beam. With tubesof this type a multicolored image, such as a television image, can'be produced by the viewing screen when electron streams of 20 kv. energy and 10 kv. energy, reapectively, are modulated in intensity in accordance with the' yellow and blue color content of a signal image, respectively, and are swept in unison over the viewing screen ina scanning raster. Tubes of this type offer advantages of greater electron eiciency than most other color cathode ray tubes and, in addition, do not require any, physical alignment between image elements of the screen and other apparatus. a

When electron beams of dilferent velocity are deflected electrons comprising the beam from the rst electron gun. The result is a pair of concentric electron streams, one traveling at a low velocity corresponding to, say, 10 kv. and the other travelling at a high velocity corresponding Vto 2.0 kv. energy.

In accordance with one preferred form of the present invention, the substantially coincident low and high velocity electron streams pass into the zone of influence of a set of magnetic deflection coils immediately upon issuing from the second electron gun. These coils receive saw-tooth sweep currents that impart scanning movements to the electron beams, the lield values being such as to deflect the respective beams to a somewhat greater extent than is required for the size of the raster to be scanned. An electron lens is located substantially coincident with the magnetic deflection coils. The lens receives a time-v independent voltage tending to deect the electron beams towards the axis of the tube and to an extent determined by the initial deflection of the electron beams from the tubeV axis` and their respective velocities. The electron Y lens` voltage is chosen to deflect the ray beams in the bytheA same deflection elements (whether electrostatic or magnetic) the deflection `depends upon the velocity of thewibeams. In consequence, it is not possible, in prior cathode ray` devices of this type, to sweep the beams tol like extents by any single set of dellection elements. In accordance with the one aspect of the present invention,.this difficulty is overcome and the beams Vare converged at the viewing screen by the action of two types of` elements. One set of elements serves as the main deecting system` and sweeps the'electron beams in usual fashionv overthe viewing screen to define the scanning raster. 'Iliis deiection system may introduce some divergence between, the respective beams. .The secondV set of elements serve primarily as ,differential deflecting elements to compensate for'` any divergence of the beams under the influence of the 4irst elements. The electron beams accordingly issue from the neck-like portion vof the tube as a substantially coincident` pair of high and low` velocity beams, they are deflected by the firstV and main deflection elements to execute sweep movements and are collirnatedv at the viewing screen by the action of .the second deecting elements. v

In accordance with another aspect of the present inventionthe plural cathode ray beams 'are concentric in relationship, facilitating coincidence at the viewing screen. Onebeani is generated by aV rst electron gun which imparts an initial energy of; say, a 10 kv. to the electron beam. The second electron beam is generated by a second electron gun throughA which the rst beam travels. 'gunimparts a total energy of, "say, 1() kv. tothe Y lectrons thereof and ani additional 10 kv. energy-to the convergingdirection in amount` suiiicient Yto overcome the diverging deflection associated with the action of the time varying magnetic fields. The beams-accordinglyV substantially converge on the viewing screen under all sweepconditions. f s 'Y i An alternative embodiment of thei present invention likewise uses magnetic `dellection coils. In this instance, however, the electron beams are converged by electrostatic dellection plates which also receive time-varying sweep voltages. The latter voltages are in direction and amount to overcome the diverging elects of the magnetic tields. The electron beams accordingly converge substantially on the viewing screen despite @the diverging effects of the magnetic sweep coils.

It is therefore an object .of the present invention to provide an improved color cathode ray image displayv system ofthe multi-energetic electron beam type in which a two-part deflection system serves to deiiect the electron beams while maintaining their coincidence at the viewing screen.

' Still another object of the present inventionisto pro- Yet another object of theV present inventionis to provide an improved apparatus for generating a p'air of concentricV cathode ray ibeams having dilfering velocities, and for accelerating such beams toa viewing screen Where diiferent colors of light are produced thereby.

Still another object of the present invention is-to provide an improved apparatus fordeveloping acomposite electron beam composed of high'energy electrons and low energyelectrons in which the low energy electron component is modulated in iris-like fashion to vary Vthe value thereofwithoutY affecting the 'high energy component.

Another object of the present invention is to provide an improved multicolor cathoderay tube imagedisplay system in which electron beams of unlikev velocities are created in substantiallyV concentric relation, rthe beams are vide` a system of the foregoing typehaving features of Y construction, combination Vand arrangement by` which Ya highly elfective satisfactory multicolor cathode raygima'ge Y Yis produced at a minimum sweep power requireme'ngwitlr aA minimum of apparatus, and in a manner giving rise to an image that is sharp, devoid of pattern effects, and is produced with high efficiency.

The novel features which I believe to be characteristic of m'y invention are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings in which: Fig. 1 is a somewhat diagrammatic view with parts broken away of a Penetron multi-layer type color cathode ray tube and the associated energizing devices constructed in accordance with a preferred form of the present invention;

F Fig. 2 is a cross-sectional view through axis 2-2,

Fig. 3 is a greatly enlarged view in axial cross-section of the electron gun and sweep mechanism of the apparatus of Fig. 1 with energizing devices shown in diagrammatic form;

Fig. 4. is a diagrammatic representation of the paths followed by the respective electron beams of the apparatus Y of Figs. 1-3;

Fig. 5 is a view, generally like Fig. l and showing an alternative embodiment vof the present invention; and- Fig. 6 is a fragmentary cross-sectional view through axis 7..-7, Fig. 6.

The overall image display system The image display system includes a cathode ray tube indicated' generally at 1,'Fig. l, having a neck-like portion 2. of elongated cylindrical conformation. At one end of theneck-likeV portion 2.,l the tube has a base 3 of conventional type with prongs to be received on the mating socket provided for the circuit connections to the tube. As shown, the tube flares out in the bell-shaped portion 4 andl at its extreme other end has a face plate 5 which may be somewhat curved as shown. Preferably, the neck 2, the bell 4, and face plate 5Y of the tube are all of glass. The interior of the tube is evacuated to define a space within which the electron streams may be developed and through which they travel without substantial losses.

The faceplate 5`of tube 1 serves as a viewing screen. Onits inside surface this face plate receives the phosphor coating 6. This coating is of materials which produce light when struck by the electron beams. To this end, the coating 6 is inthe form of at least two layers, one being responsive toV electrons of one energy range and the other being responsive Vto electrons of a different energy range. For example, the layer adjacent the base 5 may be composed of zinc sulfide activated with approximately 0.1 wt. percent Asilver to produce a blue image when struck by electrons having energies ranging from say, 10 to 20 kv. The second layer, facing the neck portion 2 of the tube, may, for example, be of zinc cadmium sulfide activated with approximately 1.0 wt. percent ofmanganese to produce aV yellow fluorescent image when struck by electrons having a range of energies of from l 'to 10 kv., for example. The latter layer passes the higher energy electrons without substantial resistance or light production. While, as set forth herein, the multi-energy beam may be composed of two components, each of which may vary over a range, for ease of presentation in the description and claims, the two energy components will be treated as specicxed energies. Thus, for example, in the above example the high energy component will be referred to as a 20 kv. beam and the low energy component as a 10 kv. beam.

The specific arrangement ofthe uorescent coating 6 forms novpart of -the present invention. It is suflicient to note that it Vmay be of the two-layer construction described above or, in the alternative, may be of someother construction Vcapable of producing light of one color kwhen struckbyk a beam of one velocity electrons and a dilerent .color when struck-by a beaml of another velocity electrons. Y

The neck portion 2 of the tube 1 receives the electron beam forming and accelerating devices. These are shown generally at 7, and 8, respectively, Fig. 1. The electron beam forming mechanism or electron gun 7, as hereinafter described, forms an electron beam of circular crosssection which, in the absence of deflection, travels along the axis X--X of the tube 1. Also as hereinafter dcscribed, this beam forms the high velocity, high energy component of the composite electron beam. The second electron gun, indicated generally at 8, includes centrally aperturcd elements which permit the electron beam from gun 7 to pass therethrough. This gun generates a low velocity electron beam of generally circular cross-section which merges with the electron beam from gun 7. Thus, the two electron guns serve to produce a composite electron beam having a high velocity portion from the gun 7 and a low velocity portion from the electron gun 8. In the absence of deflection the electron streams are directed along the axis X-X. While it may seem improper that the two beams of different energies and velocities generated by electron guns 7 and 8 should merge and occupy the same space, experiment has shownthat this arrangement is entirely proper. Actually the elec'- tron density of both beams is so low that the two beams'r readily occupy the same space at the same time with no detectable effect upon one another.

i The electron gun 7 has a control electrode 9 that modulates or varies the intensity of the electron stream v in accordance with an applied voltage. This electrode is supplied with a time-varying voltage from the' blue signal source 10 to vary the intensity of the electron beam from gun 7 in accordance with the modulation or signal information to bel imparted to the blue beam as it is swept in a scanning raster over the viewing screen. Similarly, the electron gun 8 has a control electrode 11 which varies the intensity of the electron beam produced by that gun in accordance with applied. voltage. The control electrode 11 receives voltage from the yellow signal source 12 to modulate or vary the intensity of the second electron beam with time in accordance with the yellow signal information.

As hereinafter described in further detail, the electron streams from guns 7 and 8 travel into the zone of influence of the vertical sweep windings 13` and the horizontal sweep windings 14 promptly upon issuing from the electron gun 8. These windings receive time-varying sweep current from the sweep current source 15. This source produces two time varying currents, one for the vertical coils 13 and the other for the horizontal coils 14. For example, for a television display system the vertical coils 13 may receive a saw-tooth current wave having approximately sixty repetitions per second, whereas the horizontal windings 14 may receive a` saw tooth current Wave having a repetition rate of approximately 13,000 per second. These act on the issuing electron streams to deflect them in unison (but not always to the same extent) to execute a television image raster across the screen 5, thus energizing the phosphor coatings 6.

As described hereinafter in detail, the electron streams may be deflected differentially by the action of the sweep coils 13 and 14, so that the coincidence of the two electron streams may be destroyed by the action of these windings. In accordance with the present invention, this difculty isrovercome by beam converging elements which serve to restore the coincidence of the electron beams by the time they reach coatings 6. In the form of the invention lshown in Fig. 1, the supplementary elements include the conducting sleeve 16 which is charged in relation -to the electron Vgun 8 by the unidirectional voltage source 17. This sleeve defines a convergent electron lens active upon; the deflected electron beams to restore their coincidence. In the alternative construction of Fig. 6, a timevarying electric field is used for the same purpose. Whilel electrostatic lens may be formed with a positive potential applied to sleeve`16 as well. 'i l VThe high-speed electron gun 7 The constructionY of the electron gun 7 is shown in "detail in Fig. 3. VIn this figure, as well as Fig. 1, the variousmechanical support elements are omitted'to show the construction of electrical elements more clearly. As shown, -the electron gun 7 includes an electron beam yforming `mechanism 18. `This mechanism includes a nected to a prong of the base 3 (Fig. 1), and thence to the cathode biasvoltage source, represented generallyrby battery 26and voltage divider 33. Connection thereto'is represented schematically by conductor 23. t

.As shown inY Fig. 3, a beam-deiining focusing electrode 24 Vsurrounds the cathode 21 at its forward end. -This electrode likewise has a conductor 2S whichis connected to a prong in base 3 and thence to external Vcir cuits; However, for purposes of illustration, `and to indicate Vthe`relative`valuesV o'ftheelectrode energizing voltages,"th`e ,electrode 24 andaconductor 25 are shown connnected to.` the illustrative unidirectional v'oltage source 26 so as to maintain electrode. 24 negative with respect-to cathode 21. A weak converging lens is delined with accelerating. anode 31.by the sleeve-shaped anode electrode 27 which is connected to. source 26 to receive a positive voltage in relation to the electrode 24.

This anode electrode serves .toA unify the electron beam and minimize its 'own divergent tendencies. The electron beam isalso shaped by the electric eld established between focusing electrode 24 and first accelerating anode 28, which has a small circular aperture which may, for example, be about 0.028" Vin diameter. diate the electrodes 24 and 27, the electron beam passes through the aperture in the control electrode 9, which `aperture-may, for example, be 0.060in diameter.; AsV

above described with reference to Fig. 1, electrode receives a time-varying voltage from the `blue `signal `source 10 and thereby -tserves to control `thejintensity or electron density ofilhe electron beamproduced by'elec-` i Y 50 directional bias voltage-. fromsourc e26 through the tron gun A7. The control-electrode 9 receives a, uni-V Also intermed medium of the conductor `249. Cathodev gun V7 is described in greater detail in U.S. Patent 2,852,716 to I. M.

The net eiect of the above described elementslof the VAelectron gun 7 4is to produce a smalldiameter,'circular cross-section electron stream having its `electron density varying with time in accordance with the time varying signals from blue signal source 10 `and having a l.velocity determined by the portion `of the `voltage. of sourcev 26 thati's applied to the electrode 31 that is, forexample, l0 Vkilovolts positive ingrelation to the cathode 21, thus giving the electron stream 30 to 10 kilovolt ,energyV and the corresponding velocity as it emerges fromanode 31; 'I'his electron stream is illustrated at 30, Fig. 3.,. It' may, for example, have an effective Vdiameter oftheforder of 0.020 as the `beam passes through cathode 38. d

A suitable magnetic centering device 34 is` received over theneck-likeV portion of the tube 1 `in registration withgthe electron gun 7. This provides adjustment of, the axial `position and direction of the electron beam, 30.

bThisdevice forms nopart ofl the present inventionjand maybe one of manyvsuchl'pldevices well known to i the nIt may', for example, consist` of aI-painofxannular i lit-agee?? 2121?, juxtaposed `relatie11.51.1112, an@ relatively.

A The low-speed electron gun 8 The electron YgunV 8 is generally similar to electron gun 7. Electron gun 8 diiers from electron gun 7 primarily in'that all of the elements of the former have unobstructed central openings of suiiicient size to pass the electron beam 30 from gun 7. Such openings may,` for example, be of the order of 0.030" in diameter or more. In addition, the electron beam forming and accelerating elements of gun 8 are adapted to form a low energy electron beam and to accelerate the two beams.

More particularly, the electron gun 8 has a heater 36 which iswound in reversed spirals similar to those of heater 19, but of increased diameter to pass the beam 30. Thisheater is received in the cathode sleeve 37 which, atits" forward end, has a concave spherical annulusV Scoated `with electron emitting material. Cathoder37 is electrically connected t0 accelerating anode V31. A focusing electrode "39, similar to electrode 24 Vof gun 7, surrounds ther end of the cathode 37 and, as shown, is connected to the unidirectional voltage source" 17, and maintainedata potential negative with respect to cathode 37. ".Thesfej elements, together Awith the iirst accelerating anode '41, serve to produce a low voltage electron stream 42 merging with the high voltage electron stream 30.'V The control electrode 11 is located adjacent the anode 41 andis connected by conductor 44 to aportion of the voltage from source 17 to provide bias. Resistances 43 isolate modulatingY electrode 11, as well as 9 from the bias sourceto allow the applied signal voltages to be eiective. lControl electrode. 11 also receives a time varying voltage from the yellow signal source 12, and thereby serves to modulate or vary the electron density in the stream 42 in accordanceV with theV time variations of the voltage from source 12. However, theV control electrode V11 does not significantly vary the electron density or" the beam 30 because that beam is fully formed and developed andV is traveling at a velocity corresponding to its 10 kilovolt energy when it enters cathode 38. Consequently, the negative signals applied to control electrode 11 are ineffectual to Vchange the electron density of beam 30. In contrast, the beam 42 is traveling at a relatively low'velocity and the electric field of the elec-V trode `11 is eiective in controlling the electron density of electron beam 42. The modulating action of electrode -11 up0n-beam42 is similar to that of a cameraVV iris in that the marginal electrons are iirstV arrested and increased negative voltage cuts oit successive radially inf ward portions of the electron stream. Thus', the beam 42can be wholly cut 0E by the electrode 11 while beam 30 is substantially unaiected.

. VAfter passing through the control electrode 11, the

2 composite electron beam passes through anode 4S, which is similarY to electrode 27 ofpelectron gun 7 andV denes, with anode electrode 46, a Weak converging lens. 'The beam isthenvaccelerated by anode electrode 46. This electrode is lconnected to a point on the source 17 giving, for example,"a 10 kilovolt acceleration in relation to the cathode 37. Electrode 46 is connected to coating 51 upon the interior of tube V1 by a spring member 52 and a metallic collar member 53. Coating 51 may be a colloidal suspension of graphite inwater and, by ap- V.plying the Vaccelerating voltage of electrode 46 along the entire path of the composite electron beam, continues. to accelerate a-nd prevent divergence of the beam; 1 Ihexactionofanode electrode 46 in conjunction with the cathode`37 and electrodesV 39'and 45, 'is to acceleratei the `electro'nbe'am 30k by the same voltage asis impartedvtobanlAl. l `In the. specic illustrationV shown, Y

therefore, the electrode 46 serves to accelerate the electron beam 30 by an additional 10 ikilovolts, thus imparting to that electron beam a total energy of kilovolts and the corresponding velocity.

. A beam centering device, such as that shown generally at 47, may be providedl for the electron gun 8. Such a device may be any one of the many constructions known to the art, such as the unit 34 above described. It will be observed that the action of the centering device 47 is effective on both of the electron beams 30 and 42, although the extent of the deection effected by this device is diterent for the two electron beams because of their diifering velocities.

The magnetic deflection mechanism Upon leaving the electron gun 8' (Figs. 1 and 3) the composite electron beam passes into the magnetic eld of the vertical deiiection windings 13 which straddle the space traversed by the electron beams. The beams similarly pass into the magnetic lield of the horizontal deection windings 14. Current flow inthe vertical deection windings 13 produces a magnetic field having a horizontal direction transverse to the tube and of substantially constant ux density over the area traversed by the electron beams. Similarly, current ow in windings 14 produces a vertical magnetic iield of substantially constant flux density over the area traversed by the electron beams and transverse thereto. .The fieldv produced byy windings 13, because of its horizontal orientation, deilects the beams inthe vertical direction. The 'lield produced by the windings 14,. because of its vertical orientation, deilects the beams in the horizontal. direction. The windings 13 are energizedwith a sawtoothcurrent wave of, for example, 60 repetitions per second. The windings 14 Vare energized with a saw-tooth current wave of, for example, 13,000 repetitions per second. The combined action of the windings under these respective sweep currents is to sweep the beams in a series of horizontal sweeps or lines across the viewing screen, with the vertical positions of the lines progressing in saw-tooth fashion up the screen to scan the entire television image, thus executing a television scanning raster.

g It can be shown that the amount of the beam deiiection associated with current flow in the windings 13 and 14 is inproportion to the current value in the windings (and hence the magnetic field density) and is inversely proportional to the square root of the electron beamaccelerating voltage. ln other words, if the beam (Fig. 4) is accelerated by a voltage of 20 kilovolts and the beam 4Z (Fig. 4) is accelerated by a voltage of 10 kilovolts, the beam 42 will be deected by the current flow in-windings 13 and 14 to an extent about 40% more than the ray beam 30. Accordingly, while the action of the windings 13 and 14 is to deflect the ray beams in unison horizontally and vertically across viewing screen 5, the beam 30 tends to be deilected to a lesser extent thanvthe-beam 42. Thus, in the absence of other deecting inuences, the beam 30 scans an area of smaller size than the beam 42. In the case of a conventional television deilection raster the beam 30 will execute a raster that is a smaller rectangle than that of the beam 42.

.The beam converging mechanism of Figs. 1 and 3 In the apparatus of Figs. 1 and 3, beams 30 and 42 diverge' under the action of the windings 13 and 14. This k divergence is compensated by the beam converging action of the electron lens dened by the conducting sleeve 16m conjunction with the anode 46. The negative voltage-applied to the sleeve 16 in relation to the anodev 46 establishes an electrostatic field 'having the general shape indicated by the lines l48 (Fig. 3). It will be noted that the influence of this field on the electronsrvaries ywith the extent the electrons-depart from the axis X;X, the effect beinggreater with -increased departure of the electron streams from the axis. The resultant deiiection of the beams is towardsthe axis X-X, and hence is in direction opopsite theinitial magnetic rayV beam delection.

The extent of the electron beam deection by the electron lens action of the sleeve 16 and the anode 46 is determined by the joint values of the respective beam velocities and the distance the respective beams depart from the axis X-X. lt can be shown that the deflection oi an velectron beam under the influence of an electrostatic iield is inversely proportional to the energy of the beam and proportional to the electric field strength. Thus, the deilection of the beams (assuming that they follow like paths of travel through the anode 46 and the sleeve 16) is two times as great for the l0 kilovolt beam as for the 20 kilovolt beam. The fact is, of course, that the two beams do not follow like paths of travel, for the initial deflection of the 10 kilovolt beam under the action of the magnetic fields is about 40 percent greater than that of the 20 kilovolt beam. In consequence, the actual converging deilections of the 10 kilovolt beam under the inuence of the electron lens are greater than the detiections of the 20 kilovolt beam, in part by reason of the initially greater l0 kilovolt beam deilection and in part by reason of the lower velocity ot the 10 kilovolt beam.

By proper choice of electron lens effect-and specifically the voltage between the sleeve 16 and anode 46- it is possible to restore the convergence of the beams at the viewing screen under all sweep conditions. With this voltage value the electron lens deflects the low speed beam towards the axis X-X in an amount greater than the high speed ray beam-and the respective detiections vary with the extent of the magnetic 4ray beam sweep as required to restore coincidence. Of course, in a prac tical mechanism this perfect action cannot be obtained, but to `an acceptable practical extent the beams are converged under all conditions of sweep current in windings 13 and 14.

Since the anode 46 and the sleeve 16 (Fig. 3) are both within the time varying magnetic fields of windings 13 and 14, there is some lcendency for eddy cur-rents in these elements. If desired, these eddy currents can be reduced by slotting these elements in the manner of a Faraday shield.

It will be 'noted that the above-described converging action `overcomes the electron beam divergence without requiring any' time varying voltages or currents. This is a decided advantage since the time-independent voltage required for sleeve 16 is readily and inexpensively obtained. In addition, it is unnecessary to provide the relatively complex circuits required to produce, shape, and synchronize time-varying voltages for application to the beam converging elements. AFig, 4 shows in diagrammatic form (not to scale) the paths of beam travel in the tube of Figs. 1 3. As shown, the beams 30 and 42 are coincident and on X-X'as they pass -into the iield of windings 13 land 14. Under'the action of the windings 14 alone, the beam 42 is deected to a greater extent than ray beam 30, as, for example, indicated by the dashed lines applicable to ray beam 42 and to ray beam 3l?, respectively. However, electron lens -action serves to deflect theA two beams toward the axis X-X and deilects beam 42 to an extent greater than beam 30. Accordingly, instead of followingthe dashed lines of paths of travel shown in Fig. 5, Athe beams follow the solid line paths as indicated and converge at the viewing screen 5. Y

It will be noted that magnetic sweep coils. 13`and .14 act on beams and initiate deection Yof the. same before the beams are subjected to'elect'non lens action. This `is necessary to take advantage of the converging action of the electron lens. Italso provides some of the selective action-of the electron lens since the initial deection of the 20jkv. electronlaeam.

It is not necessary however, that thebeams undergo all l,

of the magnetic deectionbefore being acted upon by the electron lens, since, as shown in Fig. 5, the electron lens may be arranged to overconverge on its Vown zone of inlluence, permitting further diverging magnetic action asshown while nevertheless bringingv the two beams to coincidence on the viewing screen.

' The system of Figs. 5 and 6 Figs. and 6 are views generally like Figs. 1 and 2, but showing an alternative form of the present invention. Parts corresponding tothose of Figs. 1-3 are indicated .by like reference numerals on Figs. 5 and 6. In the apparatusofFigs. 5 and 6, electron gun 7 coacts with blue signal source v to produce a high energy electron beam having its intensity varying with time through the action of control electrode 9. 4This beam'has an initial energy Aof 10 kv. Electron gun 8Nacts in conjunction with yellow signal source 12 to produce Ylow energy electron beam modulated by control electrode 11 inaccordance `Withrthe Vtime variations of the yellow signal. This electrou `beam is coaxial and concentric'withthebeam from lgun 7. Electron vgun 8 serves to'aecelerate thebeam so formed by 10, kv.v and toimpart additional l0; kv. acceleration to the `electroribeam 30`produced by electron gun 7'. 'Ihe beams issuingpfrom electron gun 8 are deilected in unison (but to different extents) by magneticsweep windings 13 and 14. 'I'hese are energized by sweep voltagesource 15 and'serve towdellectthe electron beams as above described in connection with theA lapparatus of Figs. Ils-.3.1 described above, the action of `the magnetic elements is to dellect the `10.kv. beam from electron gun ',8 to anextent labout 40 percent'greater than the 20 kv. beam, thus giving the electron beams diverging directions in relation to each other while deliecting them in unison. The system .of Figs. 5 and 6 includes vertical electro` `static deection plates 49 and horizontal electrostatic deilection plates 50. Voltages from sweep voltage source "51 are applied to these respective ysets of plates to sweep the beams in converging relationship (-as compared with the diverging eiects of windings 13 and 14) ashereinafter described. Sweep voltage source 51 applies avoltage across the horizontal plates '49 that Tis of saw-tooth jshape' having afrepetitionV rate of, for' example, 60per secondhand in synchronism` the s'awftooth current applied to vertical dellectingwindings ,13 bysweep current source ,15.` Similarly, sweepvoltfage source 51 apimpart divergence to the electron beams. This divergence is overcome, and vthe beams are caused to coincide on the viewing screen, by the action of other elements that are elective in opposing diierential fashion on the two `electron beams. In the form of Fig. 3 these elements are an electrostatic electron lens which receives only the time-independent voltage required for lens action. In the form of `Figs. S and 6, these elements are a separate electrostatic deflection system. In each instance, the action of the main deflection system is opposed to some extent by fthe secondary deflection system, but theeiect is greater on the low speed beam than the high speed beam by an amount that overcomes the divergence pro duced by the magnetic action. The net elect is to delleet the rayV beams while maintaining their coincidence at the viewing screen.

p While the described embodiments include converging means so as to render the devices and systems thereof completely operative under all circumstances these means are not essential in all embodiments. Thus, for example, screen 5 maybe formed of transparent phosphor lms,

' the optimum excitation energy of which are so close toplies" a"y voltage across `vertical"plates" 5,0 having saw-tooth shape" and having wave shapeand repetition rate like the current PPlied to and in synchronism tristement. 1

are'of polarity to deflect the beams in `'DlvPOSite sense to thefdelle'c'tions associated with the current flow in windings 13 and 14. 4The amount' of such opposed deliection, however, varies in accordance with the beam velocities and can be Yslii'J'Wn to be substantially inversely propor-v tionaltothe energiesfof thekray'beams. Thus, thel() kV, `electron beam deil'ected abouttwo times as much actual voltage applied to'the electrostatic deflection plates by sourceSly is chosen to impart a converging travelto Vtherespective beams that foisets the diverging action of magnetic ray beam deecting coils 13 and 14. Accordingly, Vthe bea-'msare` caused to converge at least at phosphor coatings', Fig. 6, and'thus are swept in flected byV a main set of' dellectionV4 elements which Ymay 1, The` vdltages applied' byjsource 51 to plate's419 and gether that little divergence of the electron beams is encountered in the deflection thereof. While the apparatus specifically described herein utilizes two constructions for the purpose, it will ofcourse be understood that other arrangements may be used.

"Ir'he'electron eiciency of the multicolor image display system of the present invention is very good, especially Vas cornpared with system using beam intercepting elementsfof one kind or another. In thefpresent system es-v sentially all of thefelectrons passing from electron gun 8 are' eiectiye 'in striking the viewing screen and .producing light from one phosphor or the other, It will also be noted that there `is no need to separate Ythe various color components of the electron beams on a time basis or to produce switching voltages required-forselection bewithonecolor signal and the elect-ron beam from electron g'un `8 is modulated 'in`accordance'- with the other color signal and no auxiliary `switching means is required. It

is, accordingly, unnecessary to provide color switching systems operating at -very high frequencies, such as 'the megacycle lswitching signals required for someV forms of color `television image presentation. i

The above description is based upon'a specific set of electronbeam accelerating voltages and a specic set of colored light producing phosphors. It will, of course, be understood :that the specific voltages and the specific phosphors form .no part ofthe present invention and thatfother vol-tagesv and other phosphors can be used, if desired;V Similarly, while the' ab'ove description refers to deflection of the beams in a television image raster,Y it willrbe understood that .the apparatus of the invention is Vadapted to other forms of'beam deflection and image display including, for example, radar image display systems. Additionally,. although 'one speciiic `structure has been shown as the preferred embodiment of electron guns 7 and 8, the broaderaspect of theA invention includes any pair of electron guns adapted to provide vconcentric electronY electron gun- 7., As used in the instant specieation and theappended claims, the vwords concentricl and coaxial ar'eintended to loe/ descriptive of both vthe arrangement wherein twodifferentrelcitv. beamlsgmronenfsfoscupy the same" space :and are collinear"andthe arrangement lin which, one`I component hasv an annularcross-seet1onaud surrounds the othercomponent.-

,. Electron beams 30 and 4Z have total current values of a few milliamperes. Consequently, the space actually Occupied by the electrons in each isvery small in relation to the total space occupied by the beams. In other words the electron densities are very low. The respective beams can, accordingly, cross, separate, and converge without a substantial number of electron collisions or substantial interaction between the beams.

While I have shown and described specific embodiments of the present invention it will of course be understood that various modications and alternative constructions may be made Without departing from the true spirit and scope thereof. Thus, for example, the two-part deection system, in addition to the disclosed embodiments, could be comprised of a rst, electrostatic deflection system supplied with a time-varying voltage, and a second, electromagnetic deflection systeml supplied with a time-independent voltage. I therefore intend,` by the appended claims to cover all such modifications and alternative instructions ias fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A multicolor cathode ray image display system comprising in combination: a cathode ray tube having an axis; a plurality of electron guns operable to produceelectron beams substantially coincident with `said axis and of differing velocities, and a viewing screen ylocated along said axis and having phosphorsresponsive to electron beams of said velocities, respectively, to produce illumination of differing colors, respectively; magnetic means operable to sweep said beams in unison across saidviewing screen, said means diverging said electron beams; and secondary deflection means operable to deflect saidV beams differentially, in sense opposite to the diverging deflection of said beams under the irnluence of the magnetic means, and in amount to restore the substantial coincidence of the beams as they reach the viewing screen.

2. A multicolor cathode ray device comprising in combination: an evacuable envelope having a faceplate at one end thereof and a neck-like portion at theother end thereof; a plural layer phosphor screen upon said-faceplate and including a first layer of phosphor adapted to emit a iirst color light when excited by a beam of electrons having a rst velocity and a second layer of phosphor adapted to emit a second color light when excited by a beam of electron beams having a second'velocity; means within said neck-like' portion generating a rst beam of electrons; means within said neck-like portion generating a second beam of electrons concentric with said rst beam of electrons; and meansto accelerate said beams to said rst and said second velocities respectively to cause the emission of said colors from said phosphor screen. Y

3. A multicolor cathode ray image display system comprising in combination: a cathode ray tube having an axis, at least two electron guns operable to produce electron beams substantially coincident with said axis and of differing velocities, and a viewing screen located along said axis and having phosphors responsive to electron beams of Isaid velocities,respectively, to produce illumination Aof dilfering colors, respectively; magnetic sweep means operable to deflect said beams and diverging the same, and means dening a convergent electron lens operative on said beams after at least partial deiiectionby said magnetic means and in amount to maintaingthe coincidence of saidray beam-s at the viewing screen. g Y 4. A multicolor cathode ray device comprising in combination: an evacuable envelope having at one en drthereof a faceplate and at the opposite` end thereof a neck-like portion; a plural layer phosphor screen upon said faceplateand including a rst layer of phosphorfadapted to emit a rst color light whenexcited by abeamof electrons-having a iirst velocityV and a second layerofphos-4 yphor adapted to emit a second color when :excited-by a beam of electrons havinga second velocty;means within said neck-like portion generating a iirst electron beam; means within Isaidfneck-like portion generating a second beam of electrons concentric with said first beam, said last named means having an axial passage therethrough to permit unobstructed passage of said rst beam therethrough; means accelerating said beams to said velocities to cause the emission of said colors from saidy phosphor screen, and means for deecting said rst and said second electron beams in coincidence over said faceplate in a predetermined pattern. Y 'i 5. A multicolor cathode ray image display system comprising in combination: a' cathode ray tube having an axis, at least two electron guns operable to produce electron beams substantially concentric with said axis and of differing velocities, and a viewing screenlocatedalong said axis and having phosphors responsive to electron beams of said velocities, respectively, to produce illumination of differing colors, respectively; magneticsweep coils operable to produce sweep magnetic elds crosswise of said electron beams; means to energize said sweep coils to sweep the ray beams by magnetic action. across said viewing screen while imparting divergence thereto; and means dening a time-independent beam deecting tieldwith increased beam deflection action away from said axisV and of direction to deect. said beams toward said axis, said eld being active on said electron beams after they enter the eld's of said sweep coils and having variations in strength of amount Vto Yrestore the coincidence of said beams at the viewing screen. Y

6. A multicolor cathode ray imagedisplay system cornprising in combination: a cathode ray tube having an axis; at least two electron glms operable to produce electron beams substantially concentric with said axis and of differing velocities, one of said guns terminating in a conducting sleeve on said axis through which both beams emerge, and a viewing screen located on said axis and having phosphors responsive to electron beams of said velocities, respectively, to produce the emission of differ.- ing colors, respectively; magnetic sweep coils operable to produce sweep magnetic elds transverse to said electron beams, said elds being in the path of the electron beams as they emerge from said sleeve; means to energize said sweep coils to sweep said beams by magnetic action across said viewing screen Ywhile imparting divergence thereto; a conducting sleeve on said axis of greater diameter than said rst sleeve, telescoped in Apart over the end of said rst sleeve, and extending into the contines of said sweep magnetic elds; and means charging said last sleeve in relation to said rstgsleeve in arnountto restore the coincidence of` said beams atl thev viewing screen.

7. A multicolor cathode ray image display system comprising in combination: a cathode ray tube havingV an axis, at least two electron guns operable to produceelectron beams substantially concentric with said axisandof differing velocities, means defining electrostatic deflection plates veffective on said beams, and a viewingiscreen located along said axis. and having phosphors responsive to electronibeams of said velocities, respectively, to produce illumination of diiering colors, respectively; l,magnetic sweep coils operable toproduce Ysweepmagnetic elds transverse of said electron beams; and meansto energize said sweep coils and saidelectros'tatic deection plates with time varying currents and voltages, respectively, of like wave shapesto sweep said-beamsiby magnetic action across said viewing screen and to converge said'beams by electrostatic action in amount and sense to overcome the beam divergence' associatedwith said magnetic deection action and bringsaid beams tto coincidence at the viewing screen. Y Y 8. A multicolor cathode ray image displaysystem comprising in combination: a cathodel ray tube `having an axis, 'a rst electron gun operable to produce an electron beamof predeterminedvvelocity along said axisra second electron gun operable to produce an electron beam of predetermined different velocity along said axis, said beams each having low electron density, and a viewing screen located along said axis and having phosphors responsive to electron beams of said velocities, respectively, to produce emission of differing colors, respectively; twopart means operable to deilect said electron beams in unison across the viewing screen, said means including rst parts operative by magnetic action to deflect said beams while imparting divergence thereto and second parts operative by electrostatic action and elective to deect the beams in converging direction in amount substantially equal to the diverging ray beam deflection due to magnetic action and in sense to maintain the coincidence of said ray beams at said viewing screen.

9. A multicolor cathode ray image display system comprising in combination: a cathode ray tube having an axis, a rst electron gun operable to produce a iirst electron beam of predetermined high velocity along said axis, a second electron gun operable to produce a second electron beam of a predetermined lower velocity along said axis, means operable to modulate said second beam in iris-like fashion to vary the value thereof without affecting said first high velocity beam, said beams each having low electron density, and a viewing screen located along said axis and having phosphors responsive to electron beams of said velocities, respectively, to produce emission of diiering colors, respectively; two-part means operable to deflect said electron beams in unison across the viewing screen, said means including iirst parts operative by magnetic action to deect said beams while imparting divergence thereto and second parts operative by electrostatic action and effective to deflect said beams in opposite sense to the rst deection and in unlike amounts to converge said beams at the Viewing screen.

10. A multicolor cathode ray image display system comprising in combination: means dening a vacuum envelope having an axis and a viewing screen on said axis, the viewing screen having phosphors responsive to electron beams of predetermined diiering velocities corresponding to predetermined diierent beam energies; a first electron gun in said envelope disposed to produce a first electron beam on said axis and towards said viewing screen with energy equal to the diierences between said energies; a second electron gun in said envelope disposed between said first electron gun and said viewing screen, said second electron gun having its elements apertured to pass said iirst electron beam, said second electron gun further having elements operative to produce a second electron beam concentric with said iirstelectron beam and directed towards the viewing screen; means associated with said second electron gun to accelerate both beams by the least of said energies, thereby imparting to said rst electron beam a velocity sufficient to excite one phosphor on said screen and to said second electron beam a velocity sufficient to excite the other phosphor on said screen; means magnetically operative on said beams to sweep the same across the Viewing screen; and elements electrostatically operative on said beams to converge the same on the viewing screen notwithstanding any divergence caused by said last named means.

11. A multicolor cathode ray image display system comprising in combination: means deiining a vacuum envelope having an axis and a viewing screen on said axis, the viewing screen having phosphors responsive to electron beams of predetermined diiering velocities corresponding to predetermined diierent energies; a first electron gun in said envelope and disposed to produce a first electron beam on said axis and towards said viewing screen with an energy equal to the difference between said energies; a second electron gun in said envelope disposed between said iirst electron gun and said viewing screen, said second electron gun having its elements apertured to pass said first electron beam, said second electron gun further having elements operative to produce a second electron beam concentric with said rst electron beam and directed towards the viewing screen; means associated with said electron gun to modulate said second beam in iris action to control the same without modulating said trst electron beam; means associated with said second electron gun to accelerate both of said beams with the least of said energies thereby imparting to said iirst beam a velocity suiiicient to excite one phosphor on said screen and to said second beam a velocity suicient to excite another phosphor on said screen; means magnetically operative on said beams as they emerge from the second electron gun to sweep the same across the viewing screen; and elements defining an electron lens in conjunction with the second electron gun to converge said beams on the viewing screen notwithstanding any divergence caused by said last named means.

12. 'A multicolor cathode ray image display system comprising in combination: a cathode ray tube having an axis; a plurality of electron guns operable to produce electron beams substantially coincident with said axis and of diiering velocities, and a viewing screen located along said axis and having phosphors responsive to electr'on beams of said velocities, respectively, to produce illumination of differing colors, respectively; rst means operable to sweep said beams in unison across said viewing screen, said means diverging said electron beams; and secondary deection means operable to deilect said beams diferentially, in sense opposite to the diverging deflection of Said beams under the iniluence of the rst means, and in amount to restore the substantial coincidence of the beams as they reach the viewing screen.

13. A multicolor cathode ray image display system comprising in combination: a cathode ray tube having an axis, a first electron gun operative to produce an electron beam of predetermined velocity along said axis, a second electron gun operative to produce an electron beam of predetermined diiering velocity along said axis, said beams each having low electron density, and a viewing screen located along said axis and having phosphors responsive to electron beams of said velocities, respectively, to produce emission of diifering colors, respectively; two-part means operable to deect said electron beams in unison across said viewing screen, said means including iirst parts operative by electrostatic forces to deflect said beams in a first direction away yfrom said axis while incidentally imparting divergence thereto, and second parts operative by magnetic action to deect said beams in a direction away from said axis and opposite in sense to said lirst direction and to simultaneously cause convergence of said beams and coincidence thereof at said viewing screen.

References Cited in the ile of this patent UNITED STATES PATENTS 2,442,961 Ramberg June 8, 1948 2,726,348 Benway Dec. 6, 1955 2,831,918 Dome Apr. 22, 1958 2,861,208 Benway Nov. 18, 1958 

